Visual indicating system



June 19-, 1945. L, F. MAYLE 2,378,857

VISUAL INDICATING SYSTEM Filed Jan. 16, 1945 SWEEP cmcun 7 mEcT CURRENTs AMPLIFIER INVENTOR substantially continuous surface.

Patented June 19, 1945 attests viewer. marine SYSTEM vlliouis F. Mayle,Fort Wayne, End, assigrior to Farnsworth Television and RadioCorporation, a corporation of Delaware Application January 16, 1943,Serial No. 472,572

9 Claims.

This invention relates generally to indicating devices and moreparticularly to a method and apparatus for visually measuring andindicating the sensitivity of a mosaic in a light-sensitive picturetransmitting tube.

It is common practice in the manufacture o cathode ray tubes, of thetype known as iconoscopes, to place a flat insulating member such asmica within the envelope of the tube and vaporize caesium by a processof baking, whereby it is condensed on the surface of the member to forma mosaic surface. It is diflicult to arrive at a mosaic surface ofcaesium which consists of individual islands since, in condensing, thecaesium particles become joined, together to form a after the caesium isdeposited on the mosaic member, the tube is connected to an evacuationpump while being baked whereby the tube is simultaneously baked andevacuated to vaporize and remove excess caesium from the surface of themosaic. This process continues until there are discrete islands ofcaesium and a predetermined degree of sensitivity of the mosaic isattained.

The problem of measuring the sensitivity during the baking process isdiificult as it is desirable to carry on the baking process until apredetermined degree of sensitivity is attained and this requiresconstant measurement of the sensitivity. Previous methods of measurementhave.

been found to be inaccurat and diflicult to apply.

It is the primary objectof this invention to provide a method andapparatus for continuously measuring the sensitivity of an iconoscopemosaic while the iconoscope is in the process of anufacture. 1

It is a further object of this invention to provide a cathode rayoscillograph adapted to give a continuous visual indication ofsensitivity of an tively ascertained. While the iconoscope is on thepumps and being baked, it is so arranged that a source of light may befocused to form a spot of light at the surfaceof the mosaic of the orderTherefore,

of three quarters of an inch in diameter. There is provided a chargingcircuit adapted to be periodically connected between the anode and themosaic of an iconoscope during its process of manufacture. There is alsoprovided a cathode ray oscillograph having one set of deflecting platesconnected to the charging circuit through a D. C. amplifier and theother set of deflecting plates connected to the conventional sweepcircuit of the oscillbgraph,

The charging circuit and the sweep circuit of the o'scillograph arecontrolled by a timing circuit which provides a synchronizing pulse forcontrolling the sweep circuit and a pulse of a diiferent frequency forperiodically charging and discharging the mosaic of the iconoscope. Thetiming circuit comprises two cascaded multivibrators, the first of whichis synchronized from a 60-cycle alternating current source to provide afrequency division of three and an output frequency of 20 cycles. Thisoutput is employed to synchronize the second multivibrator to provide asynchronizing pulse for controlling the sweep circuit and consequentlythe horizontal deflection of the oscillograph. The second multivibratorperforms a frequency division of is to 15 to provide in its output afrequency of 2 to 2% cycles per second depending upon the adjustment ofthe circuit constants. This'outp'ut is employed to actuate a relay inthe charging circuit of the mosaic for opening and closing it at therate of 2 cycles per second, thereby to provide a verticaldeflection inthe oscillograph, the am plitude of which varies with the chargeabsorbedon the illuminated area of the mosaic in the iconoscope. Thus, as theiconoscope is charged and discharged, there appears on the screen of theoscillograph a trace having a form repreiconoscope mosaic while it is inthe process of rounding the light spot.

sentative of the sensitivity to light of the mosaic structure.

There is also provided a glow lamp in proxim ity to the iconoscope forflood-lighting the entire surface of the mosaic, the object being toovercome the effect of leakage of charge in the area surrounding th spotof light which is utilized for illuminating the area. The glow lamp isenergized during the intervals between the two cycle pulses fordischarging the entire mosaic. Thus, there can be no error insensitivity meas v urement due to charge leakage in the area sur- Italso happens that during the baking process of a mosaic there isthermionic emission from the provided, in accordance with thisinvention, an auxiliary circuit connected to the charging circuit forbucking and eliminating the effect of thermionic currents flowingtherein during the baking process.

For a better understanding of the invention, together with other andfurther objects thereof, reference is made to the following descriptiontaken in connection with the accompanying drawing, and its scope and itssteps will be pointed out in the appended claims.

In the accompanying drawing:

Fig. 1 of the drawing is a circuit diagram illustrating an oscillographcircuit connected to the mosaic of an iconoscope;

' Fig. 2 of the drawing illustrates the configuration of the trace madeby the cathode ray in the oscillograph during one charge and dischargeperiod.

Referring particularly to Fig. 1 of the drawing, there is provided acathode ray tube I having vertical deflecting plates 2 and horizontaldeflect- 7 in plates 3. The vertical deflecting plates 2 are connectedto the output circuit of the direct current amplifier 5, the inputcircuit of which is connected to a load resistor I and polarizingbattery 8. The upper terminal of resistor I is connected to relaycontact III which is closed by the armature ll of relay l2. Armature IIand the lower contact M of relay l2 are connected .to the mosaic l6 andanode ll, respectively, of iconoscope 20.

A spot of about diameter on the mosaic I6 is illuminated by the lightsource 2|, and its intensitymay be controlledby a rheostat I8 inaccordance with the indication given by meter l9.

Relay I2 is periodically energized by a pulse generator 30 consisting oftwo cascaded multivibrators 3| and 32. Section 3| is connectedthroughconductor 34 to sweep circuit 4 which controls the potentials onplate '3 of tube I. Section 32 is connected to the input circuit of aclipper and amplifier tube 33, the output circuit of which consists ofconductors 35, 36 and relay winding l2. The multivibrator 3l isconventional in form and is synchronized from a source 29 of GO-cyclealternating current for dividing the 6.0-cycle source by 3 .to therebygenerate a 20-cycle train of impulses. The 20-cycle impulses are derivedfrom cathode resistor 31 to synchronize the horizontal sweep circuit4 ofthe oscilloscope. The second multivibrator 32 is driv n by multivibrator3| to divide the 20-cyc1e outp t by' 10, thereby generating a 2--cyclepulse,

the width of which is controlled by the value of resistor 38 and thefrequency of which is. concation of sensivity tends to result. Resistor42 is connected in series between armature II and mosaic l6, and acrossthe resistor 42 there is connected in series a resistor 43, battery 4|,potentiometer'45 and resistor 46.- -By bringing the baking oven up tobaking temperature and heat- 7 ing the tube 20 at this temperature, itis possible to measure the flow of thermionic current and adjustpotentiometer 45 to provide a bucking potential across resistor 42exactly equal and opposite to the potential resulting from thethermionic flow of current. The thermionic current are therebyeliminated in the charging circuit.

As is well known in the art, the tube 20 is connected to a vacuum pumpand baked to re- 7 move excess caesium and improve the sensitivity ofthe mosaic. Lamp 22 is illuminated periodically at the rate of twocycles per second through tubes 26 and 21, being "on during thedischarge period whenthe mosaic is shorted to the collector and oflP'during the charging period. This pro-- vides. illumination of the entiremosaic l6 of iconoscope 20 to provide photoelectrons to discharge it.The light source 2| is energized to illuminate a spot about diameteronthe mosaic IS. The mosaic is periodically charged at the rate of twocycles per second by-.relay l2. Armature II is actuated to contact Inthereby connecting resistor l and battery 8 to mosaic l6 andanode H.

Fig. 2 of the drawing illustrates at A the shape of a two-cycle pulsewhen viewed with a 20-cycle sweep. It is to be noted that pulse A has aduration of 8 or 9% of the total time of charge and discharge; therebyallowing the mosaic 91 Or 92 percent of the time in which to discharge,and insuring that the mosaic is completely discharged before the startof the next charging cycle. Armature l I of relay I2 is normally in theclosed 0 position as illustrated in Fig. 1,.thereby short trolled by thevalue of resistor 39. The relay actuating circuit including conductors35 and 38 embody a time constant circuit composed of a resistor 43 and acondemer 4|. The purpose of this time constantcircuit will beevidentwhen the operation or the circuit is described.

The mosaic I of iconoscope 23 is flood-lighted by means of a glow lamp22 which. is energized by the output of tube 26. Tube 2lis connected byconductor 23 to the multivibrator 32,

whereby the glow lamp 22 is energized at the same'rate as relay l2 butin opposite phase. The

other terminal of lamp 22 is connected to the plate supply, +131. 7

'As the iconoscope 2| is subjected to high temperatures for thepurpose'of baking the mosaic It, a thermionic flow of electrons occursin the charging circuit which includes armature I I, contact II andresistor 'l, and. therefore, a false indicircuiting male [6 fand. anodel'l through' contact I 4. When relay I2 closes contact In in response totwo-cycle pulses from pulse generator 30, the voltage transientappearing across load resistor I is amplified by direct currentamplifier 5 and applied directly to one of the vertical deflectionplates 2 of'cathode ray tube I. Since horizontal deflecting plates 3 areconnected to the horizontal sweep circuit 4 which is synchronized by20-cycle source 3|, the cathode ray beam sweeps horizontally at a20-cycle rate. Since the relay is charging and discharging themosaic ata two-cycle rate-in which the charging time is approximately 8. or 9 percent and the discharge time approximately 91 or 92 per cent, a chargingtransient will appearon the screen of the cathode ray tube on everytenth horizontal sweep and will have the form illustrated in'Fig. 2 atBand C. The height of trace B is indicative of the sensitivity ofthemosaic l6, while the initial slope of curve C is indicative of theleakage between islands of the mosaic. g

It is to be noted in Fig. 2 that there is a time diflerence between thelagging edge of the twocycle pulse A and the initiation of the chargingcurve. There is also a time difference between the lagging edge of thetwo-cycle pulse and the cessation of the charge curvejC. This resultsfrom the finite time required for the actuation of armature ll of-relayl2. The time constant circuit 40 and 4| is provided forthe purpose ofrelay l2 at the end of the two-cycle pulse. Tube 33 is normally cut-oil!because of its grid current atthe' time of the two-cycle pulse, and,therefore, during the idle period,

' baking process.

asraesv condenser ii charges to the full anode potential of tube 33. Onthe leading edge of the twocycle pulse, maximum current passes throughthe coil of relay E2 to actuate the armature into its upper position.However, thecondenser it immediately begins to discharge to a voltage dotermined by resistor to and the plate resistance of tube 33. Resistor itand the condenser as are assigned such values that the discharge ofcondenser on takes-place ahead of the lagging edge of the two cyclepulse. At this instant, the current through the coil relay it is nearthefall-out value, and, therefore, the armature of relay lilmore readilyreleases upon the lagging height of curve B indicating the sensitivityof mosaic it. It is obvious that the constant indication of the chargingcharacteristic provides a quantitative indication of the sensitivity and25 leakage of the mosaic at all times during the Furthermore, there hasbeen provided an intermittent light source for flood" lighting theentire mosaic to provide photoelectrons to discharge the mosaic whencontacts it go are closed, and there has also been provided a circuitfor overcoming the effects of thermionic emission in the mosaic circuit.

While there has been described what" is at present considered thepreferred embodiment of 3a in the appended claims to cover all suchchanges so and modifications as fall within the true spirit and scope ofthe invention.

What is claimed it:

i. In an electrical circuit for indicating the an iconoscope comprisinga photoelectric surface in the form of a mosaic disposed on aninsulating surface, a charging circuit comprisinga polarizing meansadapted to be connected to said insulating surface, relay means for con=50 necting said polarizing means to said insulating surface, a cathoderay oscillograph including a pair of deflecting plates connected to saidcharg= ing circuit whereby it deflects the cathode ray in a verticaldirection when said charging cincuit is connected to said polarizingmeans, a

timing circuit connected to said relay means for periodically energizingit and a second timing circuit coupled to another set or" deflectingplates in said cathode ray oscillograph for deflecting to said ray at ahigher rate in a horizontal direc- 2. In an electrical circuit forindicating the charging characteristic of an iconoscopemosaic,

an iconoscope comprising an anode and a pho cs .toelectric surface inthe form of a mosaic disposed on an insulating surface, a normally opencharging circuit comprising a-polarizing means adapted to beconnected tosaid insulating sur said polarizing means to said insulating Stirface, acathode ray oscillograph including a pair of deflecting plates connectedto said charg ing circuit whereby it deflects the cathode ray is Thisindication will have the confor- 2o charging characteristic of aniconoscope mosaic, do

p face, relay means for either short circuiting said 7g anode and saidinsulating surface or connecting s in a vertical direction when saidpolarizing means is connected to said insulating surface, a timingcircuit connected to said relay means for pcriodically energizing it anda'second timing cirof a mosaic disposed on an insulating surface,

a. normally open charging circuit comprising a polarizing means adaptedto be connected to said insulating surface'relay meansfor either shortcircuiting said anode and said insulating surface or connecting saidpolarizing means to said insulating surface, means for illuminating allof said surface whereby to provide photoelectrons for-completelydischarging said mosaic, and a timing circuit connected to saidilluminating ineans and. tosaid relay means for periodically energizing'and'de-energizing them in opposite phase.

d. In. an electrical circuit for indicating the charging characteristicof an iconoscope mosaic, an iconoscope comprising a photoelectricsurface in the form of a mosaic disposed on an insulating surface, acharging circuit comprising a polarizing means adapted to be connectedto said insulating surface, switching means for connecting ordisconnecting said polarizing means-to charge or discharge saidinsulating surface, a cathode ray oscillograph including a pair ofdefleeting plates connected to said charging circuit whereby itdefiectsthe cathode ray in a certain direction when said chargingcircuit is connected to said polarizing means, a timing circuit connected to said switching means fornefiodlcally energizing it and asecond timing circuit includ ing an oscillog-raph sweep circuitconnected to another set of deflecting plates in said cathode rayoscillograph for deflecting said ray at a higher rate in a diiferentdirection.

5. In an electrical circuit for indicating the charging characteristicof an iconoscope mosaic,

an iconoscope comprising an anode and a photo-=- electric surface in theform of a mosaic dismsed on an insulating surface, a normally opencharsing circuit comprising a polarizing means adapted to be connectedto said insulating surface, relay means for either short circuiting saidanode and said insulating surface or connecting said polarizing means tosaid insulating surface, a cathode ray oscillograph including a pair ofdeflecting plates connected to said charging circuit whereby it deflectsthe cathode ray in a given direction when said charging circuit isconnected to said polarizing means, a timing circuit connected to saidrelay means for periodically energizing it, a time constant circuit inthe output of said g circuit for timing the duration of each timingity-of an iconoscope mosaic when said mosaic is formed, an iconoscopecomprising an anode and a photoelectric surface in the form of a mosaicdisposed on an insulating surface, means for ll... luminating saidphotoelectric surface, a charging circuit comprising a polarizing meansadapted to be connected to said insulating surface and said anode, asource of potential connected to said charging circuit to oppose flowofcurreut therein resulting from thermionic emission from said surfacewhich occurs when said surface is heated during its formation and meanscoupled to said charging circuit for indicating the sensitivity of saidphotoelectric surface to said illuminating means. I

7. A method of indicating the charging characteristic of an iconoscopemosaic comprising, the steps 01' illuminating a certain area of saidmosaic, charging and discharging said mosaic, controlling the chargingand discharging of said mosaic to time the same at a predetermined rate,impressing the voltage transient which occurs during the charging periodacross one set of deflecting plates in a cathode ray oscillograph todeflect said ray in one direction in accordance with the charging ofsaid mosaic and deflecting the cathode ray in said oscillograph at ahigher rate in the other direction to produce an indication of thesensitivity of said mosaic;

8. A method of indicating the charging characteristic of an iconoscopemosaic comprising the steps of constantly illuminating a certain area ofsaid mosaic, charging and discharging said mosaic, controlling thecharging and discharging of said mosaic to time the same at apredetermined rate, illuminating the entire mosaic during the dischargeperiod of said mosaic to completely discharge the same, impressing thevoltage transient which occurs during the char:- ing period across oneset of deflecting plates in a cathode ray oscillograph to deflect saidray in on direction in accordance with the charging of said ,mosaic anddeflecting the cathode ray in said oscillograph at a higher rate in theother direction to produce an indication of the sensitivity of saidmosaic. v

9. A method of indicating the charging characteristic or an iconoscopemosaic during a baking period comprising the steps of charging and Idischarging said mosaic, controlling the charging and discharging ofsaid mosaic to time the same at a predetermined rate, impressing thevoltage transient which occurs during the charging period across one setof deflecting plates in a cathode ray oscillograph to deflect said rayin one direction in accordance with'the charging of said mosaic,counteracting the eflects of thermionic emission from said mosaic toprevent false indication by said oscillograph, and deflecting thecathode ray in said osciilograph at a higher rate in the other directionto produce an indication of the sensitivity-o1 said mosaic. J

' LOUIS F. MAYLE.

